Transformer



April 28, 1925.

R. V, EINGAY TRANSFORMER Filed Sept. 29. 1920 Patented Apr. 28, 1925.

UNITED STATES PATENT OFFICE.

ROBERT V. BINGAY, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOR' TO PITTSBURGHTRANSFORMER COMPANY, A CORPORATION OF PENNSYLVANIA.

TRANSFORMER.

Application filed September 29, 1920. Serial No. 413,613.

To all whom it may concern:

Be it known that I, ROBERT V. BINGAY, a citizen of the United States,residingat Pittsburgh, in the county of Allegheny and State ofPennsylvania, have invented certain new and useful Improvements inTransformers, ofwhich the following is a specification.

This invention relates to electrical transformers and particularly totransformers cooled by a circulating fluid. The object of the inventionis to provide a transformer in which the insulation between theconductors or windings is impregnated with a varnishlike compoundhardened to impart great mechanical and dielectric strength anddurability to the coil structure.

In the accompanying drawings illustrating the invention- Fig. 1 is aplan view of a transformer structure.

Fig. 2 is an elevational view thereof.

Fig. 3 is a plan view on enlarged scale of the transformer coil of Fig.1, and

Fig. 4 is a diagrammatic view in per spective of the coil formation ofthis invention.

In the transformer of this invention the windings preferably havevertical axes and the primary and secondary windings. are wound aslayers of a unitary structure having the cross section of a circle oroval. Starting at the innermost insulating barrier 3 of the windings Wwhich will be adjacent the core leg 4 of the core C there is wound onesection 5 of the low tension winding then a barrier 6 of insulatingmaterial then a section 7 of the high tension winding, another barrier 8and another section 9 of the lowtension winding, each section being ofany desired number of layers. Adjacent layers are separated by strips 10of insulating material so as to rovide ducts 11 giving access to andthrong the interior of the windings for the varnish and air dur ing theprocess of this invention and for the cooling and insulating oil whenthe transformer is in service.

The insulation around the conductors or wires is preferably of absorbentmaterial such as cotton and similarly the barriers may be of fullerboard or other material also absorbent. As illustrated in Fig. 4 theconductors will preferably be wound in open coils and with theinsulation permitting the varnish to permeate the innermost portionsaround the wire. For instance the conductors as at 12 may be wound withstring 18 leaving spaces between the wires for the varnish, or the wiresmay be wound with fabric, as at 14, adapted to absorb the varnish orboth string and a covering may be used as indicated at 15 and the stringor fabric or both may be of asbestos. Then the windings are completedthey are heated below the charring or singeing point of the insulatingor binding material. The effect of this heating is to drive off moistureand it is continued until the entire windings are thoroughly heated tothe innermost recesses which, for instance, may be in good practice 100to 120 C. for twenty-four hours. The hot windings are then subjected toa high vacuum and this together with the heat supplied by the hotmaterial rids the winding entirely of moisture and leaves it thoroughlydry.

he winding is then treated with liquid nation. The coils are then againheated to a safe temperature in the presence of air to finally drive offthe varnish diluents and to thoroughly oxidize the varnish andpermanently harden it. This hardening is usually slow and the length oftime it takes depends upon the particular type of coil and varnish used,the usual time required being, for instance, from several days to twoweeks. The open ventilated character of the windings also permits theexcess varnish to drain oil and the diluent vapors to pass off from theinterior and the air to gain access to all the surfaces so that thevarnish hardens in all parts binding the windings into a strong.permanently rigid unit. The varnish used is preferably of the typehardening by evaporation of a diluent and by oxidation; it may forinstance be composed of linseed or chinawood oils with a gum, such asrosin or copal and with gasoline or naphtha as a diluent. To hasten thefixing and hardening of the varnish a partial vacuum may also be appliedto the impregnated coil.

Each wire is surrounded by a layer of the hardened varnish impregnatingthe fabric cover or coating the bare wire and virtually results in acontinuous tube, the hardened varnish being itself a high insulation.The barriers and spacers are also impregnated and covered with thehardened varnish rendering them stiff and strong and greatly improvingtheir insulating properties. The hardened varnish also connects andbinds all the parts together against relative shifting and. this varnishhardened by this process does not soften or weaken when the transformerbecomes heated in service but remains as a permanent rigid binder andinsulator in all the parts.

After the hardening of the varnish of the first treatment furthercoatings may be applied for instance by dipping and hardening to form.protective, strengthening layers of varnish over the partsalready-impregnatedby the first treatment.

The hardened varnish produces smooth walled ducts andventilating spacesin the windings. for the free flow of the cooling fluid, and being abetter heat conductor than the oil aids in the transfer of heat from theconductors to the cooling oil. The hardened varnish is moisture proofand oil-proof and serves as a protective, insulating covering,permanently separating the conductors and preserving the cotton or othermaterial variably show a tendency to weaken when the coils heat up inservice and these compositions also become soluble in the transformeroil so as to be dissolved out, further weakenin deposit 0 sludge on thetransformer parts. The structure and method of this invention overcomethe objections of this prior practice and provide a permanentlyinsulated and durable coil structure.

While this invention has been illustrated in connection with a specificembodiment and process it is not confined thereto but is intended tocover such variations therefrom as fall within the scope of the appendedclaims.

I claim 1. In a transformer the combination with a core leg, of atransformer coil surrounding said leg and extending lengthwise thereofand comprising a plurality of successive conductor windings one withinthe other, insulation comprising strips spacing successive windingsapart to provide ventilating ducts between said windings said ductsextending from end to end of the coil, and a layer of hardened varnishforming a binding and in sulating film over the conductors andinsulation throughout the coil.

2. In a transformer the combination with a core leg, of a transformercoil surrounding said leg and extending lengthwise thereof andcomprising a plurality of successive conductor windings one within theother, insulation comprising strips spacing successive windings apart toprovide ventilating ducts between said windings and extending from endto end of the coil and communicating with at least one side of eachconductor, and a layer of hardened varnish forming a binding andinsulating film over the conductors and insulation throughout the coil.

ROBERT V. BINGAY.

the coil insulation and causing a.

